Soluble polybenzoxazole precursors are used as a resin base in thermoresistant photoresists for the preparation of highly thermoresistant relief structures, that is for the cost-effective, direct structuring of organic insulating layers. The polybenzoxazoles obtained from the precursors are distinguished by high temperature resistance, low water absorption and excellent electrical properties (c.f. EP-OS 0 291 778); therefore, they are suited as organic dielectrics in semiconductor production and also as etching masks, particularly in alkaline etching processes.
Photoresists based on polybenzoxazole precursors can be photostructured by means of conventional printing devices (contact printing or projection printing). In this case however, it is necessary for the photoresist to have photosensitive groups, respectively for the photosensitive resist to component a photoactive component. Photostructurable polybenzoxazole precursors with cross-linkable, unsaturated groups, which are used as negative resists, are known for example from the EP-PS 0 041 677. Positive resists based on polybenzoxazole precursors with diazoquinones, such as diazonaphthaquinones, as photoactive components are known from the following publications EP-OS 0 023 662, EP-OS 0 291 779 and DE-OS 37 16 629.
In the case of both of the named resist types, difficulties can arise that are caused by the photoreactive groups, respectively by the photoactive components. Namely, unsaturated groups tend to polymerize and, as a result, produce a limited viscosity stability for the resist solutions. Diazoquinones are not very thermostable and can react with functional groups, for example with amino end groups. This also has an unfavorable effect on the storage stability as well as on the reproducibility of the photolithographic process. Moreover, for processing, the sensitive photoresists require rooms supplied with yellow light in order to exclude wavelengths of &lt;500 nm.
Accordingly, it is an object of the invention to specify a method which allows highly thermoresistant relief structures to be produced simply and cost-effectively from polybenzoxazole precursors.
It is a further object of the invention to provide a method for producing highly thermoresistant relief structures without the difficulties, particularly with regard to storage stability and reproducibility, which have heretofore been encountered with positive and negative resists based on polyhenzoxazole.